Electrotechnical Systems

212 Electrotechnical Systems

of the possible inverter states gives the opportunity to receive better characteristics

compared to the two-level inverter.

It is reasonable to have different control algorithms at high (ω

m

> 0.5 − 0.55) and

low speeds. In the rst case, M, Z, and I–states are used (also H-states when T

e

>T

eref

and when there is a need to regulate the capacitor voltages [7]). One can see from

Figure 5.47 that at Ψ

s

location in the beginning of the rst sector, by choice V

k

=2

(when the torque has to be increased and the ux linkage has to be decreased), IM

torque increases very little or there is no decrease at all. If instead of the state−11 −1

that corresponds to V

k

= 2 I-state 01–1 is selected, the torque rise would be big ...